Aluminum tanning process



Patented Nov. 10, 1942 I 2,301,637 ALUMINUM TANNING rnocass Joseph G. Niedercorn, Riverside, and William 0.

Dawson, Greenwich, Conn., assignors to American Cyanamid Company, New York, N. Y., a corporation of Delaware No Drawing. Application January 31, 1941, Serial No. 376,853

Claims.

The present invention relates to the tanning of raw hides and skins and the like and has for its object to produce a white leather which is flexible and durable.

More specifically, this invention relates to the tanning of hides and skins with aluminum compounds and to a new aluminum tanning agent.

It is well known that aluminum compounds may be used in the tanning of hides and The aluminum tanning agents of the prior art, such'as alum, however, have proven unstable, and the tanning with aluminum compounds has been generally called tawing" to disinguish it from a permanent tanning. The ability of aluminum compounds to produce a fine white leather has long been recognized and hence the desirability of the use of this compound as a tanning agent is well understood in the art.

We have found that a permanent white leather of good quality may be obtained by treating pickled hides and skins with the 100% basic aluminum salts of alpha-hydroxy isobutyric' acid.

The tanning with this compound may be carried Y out under neutral, alkaline, or slightly acid conditions. Our improved tanning agent may be used alone but is preferably used in conjunction with formaldehyde or by the various synthetic tanning agents,

The following example shows how our new tanning agent may be used in conjunction with formaldehyde.

Example 100 pounds of skins having a pH of'1.5 were drummed for 15 minutes in a bath consisting of 12 gallons of water containing pounds of H2804. The pH of the liquor was 2.0. To this bath 10 pounds of formalin (37% HCHO) was added in three batches at 10 minute intervals and the skins were then drummed in the bath an additional 30 minutes. The pH of the liquor after the formalin addition was,2.1. Then 7 ounds of NaHCOa dissolved in 6 gallons of water was added to the liquor in 6 batches at. minute intervals. other two hours after which the skins were very plump and had a good feel. The pH of the liquor was 8.2, and the pH of the skins 7.6-7.8. The skins were then drained and washed for 15 minutes. iormaldehyde tanned skins were horsed up, set out and shaved. The skins were then put The skins were drummed anback in the drum and to them was added gradually 50 pounds of a 40% aqueous solution of a basic aluminum alpha-hydroxy isobutyrate Iollowed by a further addition of 30- pounds of water. The skins were then drummed for 5 hours and left overnight in the liquor. The next day they were drummed an additional 30 minutes and then washed-with water of gradually' dry, The skins, upon analysis, showed 72% hide substance, and. 5.09% aluminum as aluminum oxide.

The 100% basic aluminum salt used in our new tanning process may be prepared by adding a water-soluble aluminum compound to an alphahydroxy isobutyric acid solution and then adding to the solution an alkaline compound of sodium or potassium, such as sodium hydroxide. Sufldcient alkali must be added to neutralize the acid and to furnish an additional three moles of alkali metal per mole of aluminum present. The method of preparation of the basic aluminum salt of alpha-hydroxy isobutyrate is described more fully in our copending application, Serial No. 376,852, filed January 31, 1941. We believe that the basic aluminum salt'has the following probable structural formula HO OOC.COH(CH:)1

successively aluminum sulfate, sodium alphahydroxy isobutyrate and soclum bicarbonate.

Having now described our invention so that V the same may be understood by those skilled in the art, what we claim is:

1. The improvement in the process of tanning hides and the like which consists in subjecting them to the action of a bath containing the 100% basic aluminum salt of alpha-hydroxy isobutyrie .acid.

2. The step in the process of tanning hides and the like which consists in subjecting the same to the action of a bath containing in solution a soluble aluminum compound, alphahydroxy isobutyric acid and an alkaline compound of sodium or potassium in excess of that required to neutralize the acid. a

3. The improvement in the process of tanning hides and the like which comprises subjecting them to the action of a bath containing a conipound having the following structural formula 4. Leather tanned by the action of a watersoluble 100% basic salt of aluminum alpha-hydroxy isobutyrate.

5. Leather tanned by the action of a compound having the following structural formula.

JOSEPH G. NIEDERCORN. WILLIAM O. DAWSON.

cmrrrxcms OF CORRECTION. Patent No. 2,501,657. November 10, 19!;2.

JOSEPH c. NIEDERCORN, ET AL.

It is hereby certified that error appears in the above numbered patent requiring correction as follows: In the grant, line '4, and in the heading to the printed specification, line 6, state of incorporation of the assignee, for "Delaware" read --Maine--; and that the said Letters Patent should be read with this correction therein that the same may confonn to the record of-the case in the Patent Office.

Signed and sealed this 22nd day of December, A. D. 1%.2.

Henry Van Arsdale, (Seal) Acting Commissioner of Patents. 

